This invention relates to a scroll compressor having a restriction in the back pressure chamber tap to provide more control over the operation of the back pressure chamber.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, opposed non-orbiting and orbiting scroll members face each other. Each of the scroll members have a base and a generally spiral wrap extending from the base. The wraps interfit to define compression chambers. The orbiting scroll is caused to orbit relative to the non-orbiting scroll, and compression chambers defined between the wraps are reduced in size to compress an entrapped refrigerant.
The scroll compressor combination generally includes one of the two members being able to move for a limited axial distance relative to the other. The compression of the refrigerant between the wraps presents a separating force tending to force the two scroll members away from each other. Historically, this separating force has been resisted by tapping a compressed refrigerant to a xe2x80x9cback pressure chamberxe2x80x9d defined behind the base of one of the two scroll members. The back pressure chamber creates a force forcing the base of the axially movable scroll member toward the other scroll member, thus resisting the separating force.
While the use of the back pressure chamber does address the separating force issue, there are certain challenges that remain. As one challenge, it may sometimes be desirable to not have the back pressure chamber operable for a period of time at start-up of the compressor. As an example, under certain conditions, it may be difficult to begin movement of the compressor members. In such a situation, it would be desirable to not have the back pressure chamber operable for a short period of time after start-up. In this way, the scroll members are not in contact with each other, and there will be leakage reducing the load on a motor for driving the orbiting scroll for a period of time.
Another challenge with back pressure chambers is that during operation, there is some fluctuation in the pressure at the point in the compression chambers from which the back pressure chamber refrigerant is tapped. These fluctuations cause fluctuations in the back pressure force, which may result in somewhat non-smooth operation. Furthermore, the fluctuations in pressure also result in high pressure refrigerant flowing from the compression chambers to the back pressure chamber. Since the back pressure chamber is at a lower pressure, this gas gets expanded, then later recompressed when the pressure tap moves to a lower pressure chamber. This recompression results in a power loss. Because the restrictor minimizes the flow of gas, it also minimizes the power loss due to recompression.
The present invention presents a tap for back pressure refrigerant which has a restriction. The restriction provides a dual benefit. First, the restriction resists flow of refrigerant at start-up such that there will be a period of time after start-up before the back pressure chamber is fully operational. This provides a reduction of load at start-up. Further, when fluctuations in pressure occur during operation of, the compressor, the restrictions limit the back and forth movement of the refrigerant thus tending to level out any such fluctuations.
In one embodiment, a simple slip fit pin is inserted into the passage to provide a restriction. In another embodiment, a pin is provided with a groove. Other embodiments include a dowel with a small orifice, a hollow tube having a ball, a porous member, a screw with a slot in its threads, etc.
In general, the various restrictions provide the benefit such as mentioned above.
These and other features of the present invention may be best understood from the following specification and drawings, the following of which is a brief description.